The present invention relates generally to fluid systems, and more particularly to a flow modulating airfoil apparatus for an aircraft engine cooling system.
There are a variety of known gas turbine engine configurations, including two-spool, high-bypass engines. Such an engine typically includes a high pressure spool, a combustion system and a low pressure spool disposed within an engine case to form a generally axial, serial flow path about the engine centerline. The high pressure spool includes a high pressure turbine, a high pressure shaft extending axially forward from the high pressure turbine, and a high pressure compressor connected to a forward end of the high pressure shaft. The low pressure spool includes a low pressure turbine, which is disposed downstream of the high pressure turbine, a low pressure shaft, which typically extends coaxially through the high pressure shaft, and a low pressure compressor connected to a forward end of the low pressure shaft, forward of the high pressure compressor. A fan is also connected to the low pressure spool, forward of the low pressure compressor. The combustion system is disposed between the high pressure compressor and the high pressure turbine and receives compressed air from the compressors and fuel provided by a fuel injection system. A combustion process is carried out within the combustion system to produce high energy exhaust gases to produce thrust and turn the high and low pressure turbines, which drive their respective compressors and the fan to sustain the combustion process.
The rotation of the fan produces bypass air (i.e., air that is not used in the combustion process) that provides a major portion of the thrust in a high-bypass engine. The temperature of the bypass airflow is relatively cool compared to the engine components, so it is used as an engine cooling source. For example, a portion of the bypass airflow is bled at an upstream location into a cooling passage within the engine compartment and used to absorb heat from engine components. The cooling passage discharges the bleed flow at a downstream location back into the bypass airflow.
Two trends in new jet engine technology include geared turbofan systems and replacement of pneumatic systems with electrical systems. Such equipment can produce more heat than traditional gas turbine engine systems, so the cooling systems have increased in capacity accordingly. However, the amount of cooling required is dependent on the condition that the engine is operating in (e.g., ground idle, take-off, cruising, landing, etc.). Although effective for cooling, using the bleed flow for cooling reduces the thrust efficiency of the engine. Furthermore, in certain operating conditions, the bleed flow can cause excess cooling if left unchecked. Therefore, the amount of bleed flow being taken from the bypass airflow should be the smallest amount that provides adequate cooling during all of the engine operating conditions.